Radiator fan
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Joined: Jan 2011
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Radiator fan
Hi all. I have a 1999 coupe with 124k...couple days ago i was doing a cruise downtown. About 45 min in my temp gauge is a hair over half way. When i got home i noticed only one fan was running...and even it didnt seem to be running very fast. Any advice? Thanks.
Melting Slicks
Joined: Jan 2009
Posts: 3,275
Likes: 739
From: Miami FL
In a C5, fans can run in Low or High Speed Modes, but in each case, both fans are supposed to run at the same time.
In Low Speed Mode fans are wired in series, with half the voltage applied to each one. In High Speed Mode they are wired in parallel, with full voltage to each one.
You need to verify your fans behavior (one, both or none) in the temperature range that corresponds to Low Speed Mode AND also when the temperature goes above 235°F (again: one, both or none). If only one works, you need to identify which one.
I'm including here a description of how fans are commanded, so you can compare it to your car.
NORMAL fan operation on a C5 is as follows:
Low Speed - Triggered when coolant temperature reaches 226°F. When the coolant temperature drops to 219°F then the fans are turned OFF.
High Speed - Triggered if the coolant temperature rises to 235°F during low speed operation. When the coolant temperature drops to 226°F then the fans drop back to low speed.
With AC turned ON the cooling fans come ON in low speed mode when the coolant temperature is about 185°F. The fans remain ON in low speed mode until coolant temperature reaches 235°F, then they go into high speed mode.
If the vehicle speed exceeds 35MPH the PCM turns OFF the fans regardless of the coolant temperature. Air flow through the free-wheeling fans should be enough to keep temperatures within parameters, as long as the radiator fins are not plugged up. If they are plugged up, then the coolant temperature will rise and the fans will NOT come ON unless the car goes below 35MPH.
In Low Speed Mode fans are wired in series, with half the voltage applied to each one. In High Speed Mode they are wired in parallel, with full voltage to each one.
You need to verify your fans behavior (one, both or none) in the temperature range that corresponds to Low Speed Mode AND also when the temperature goes above 235°F (again: one, both or none). If only one works, you need to identify which one.
I'm including here a description of how fans are commanded, so you can compare it to your car.
NORMAL fan operation on a C5 is as follows:
Low Speed - Triggered when coolant temperature reaches 226°F. When the coolant temperature drops to 219°F then the fans are turned OFF.
High Speed - Triggered if the coolant temperature rises to 235°F during low speed operation. When the coolant temperature drops to 226°F then the fans drop back to low speed.
With AC turned ON the cooling fans come ON in low speed mode when the coolant temperature is about 185°F. The fans remain ON in low speed mode until coolant temperature reaches 235°F, then they go into high speed mode.
If the vehicle speed exceeds 35MPH the PCM turns OFF the fans regardless of the coolant temperature. Air flow through the free-wheeling fans should be enough to keep temperatures within parameters, as long as the radiator fins are not plugged up. If they are plugged up, then the coolant temperature will rise and the fans will NOT come ON unless the car goes below 35MPH.
Last edited by GCG; May 4, 2020 at 07:01 PM.
Melting Slicks
Joined: Jan 2009
Posts: 3,275
Likes: 739
From: Miami FL
Melting Slicks
Joined: Jan 2009
Posts: 3,275
Likes: 739
From: Miami FL
The speed modes are achieved by changing the circuit configuration. To be able to troubleshoot this we need the whole picture. Keep an eye on the temperature and when it goes above 235°F check the fans and report back how are they behaving in High Speed Mode.
